<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        div{
            width: 100px;
            height: 100px;
            /*border-left: 2px solid black;*/
            /*border-right: 2px solid blue;*/
            /*border-top: 2px solid greenyellow;*/
            /*border-bottom: 2px solid sienna;*/
            border: 10px solid red;
            /*圆角 值越大越圆 超过宽高一半为正圆*/
            border-radius: 100%;
            text-align: center;
            line-height: 100px;
        }
    </style>
</head>
<body>
<div>边框测试</div>
</body>
</html>